1. Field of the Invention
This invention relates generally to the casting of metal, and more particularly, to an improved method and apparatus for the casting of metal strip or sheet in a continuous operation.
2. Background Information
The metals industry has been developing processes and apparatus for producing an as-cast product that needs little or no additional processing such as hot rolling to reduce it to strip form. One such process that has arisen as a result of this development is the single belt casting process In this process, molten metal is caused to flow onto a moving horizontal surface in the form of a continuous belt whereupon it solidifies as it moves along with the belt. The elongated solid strip of metal is removed from the continuous belt for further processing as desired.
As attempts have been made to increase the speed of casting as measured in inches per minute of the cast strip, as well as to reduce the thickness of the cast alloys to eliminate further processing operations, several problems have arisen in connection with the feeding of the molten metal onto the belt due to the splashing and turbulence caused by the relative flow between the melt and the belt.
Normally the source of molten metal is usually spaced at some vertical distance from the belt. When the molten metal is caused to flow directly from the source of the molten metal through the vertical distance into the belt, the melt will tend to splash as it hits the belt which may result in porosity in the cast product as well induce turbulence which can cause inclusions such as oxides and folds and creases in the outer surface of the solidified strip.
The typical approaches undertaken in an attempt to solve these problems involves improvements in the feeding means such as providing a tundish between the source of molten metal and the belt. Such feeding means normally takes the stream of molten metal issuing from the source and discharges it outwardly in the direction of movement of the belt. Although this approach solves the problem of splashing, the problem of dampening of its flow to reduce turbulence still remains.
The following references contain a discussion of various delivery systems used for the delivery of the melt to belt casters.
J. Herbertson, P. C. Campbell, A. G. Hunt and J. Freeman, "Strip Casting Studies at BHP Central Research Laboratories", CCC'90 Fifth International Casting Conference, Voest Alpine, Industrieanlangenbau, Linz, June, 1990; J. Herbertson and R. I. L. Guthrie, "A Novel Concept for Metal Delivery to Thin Strip Casters", Casting of Near Net Shaped Products, TMS-AIME, pp 335-349; and J. S. Truelove, T. A. Gray, P. C. Campbell and J. Herbertson, "Fluid Dynamics in High-Speed Strip-Casting Metal Delivery System", International Conference on New Smelting Reduction of Near Net Shape Casting Technologies for Steel, SRNC-9, J. S. Truelove, pp. 1/10-11/10.